Retag audio files based on their filenames.

Given a pattern with named captures, set the ID tags for each named file based
on that pattern.

Options:

--verbose / -v
    Be verbose.

--dry-run / --dryrun / -d
    Just show what we would have done, don't do it

--pattern / -p
    Specify a Perl regex with named captures

--setonly / -s
    Limit which tags are set, e.g. "-s track" to only set the track tag,
    leaving all others unchanged.  You should be able to repeat it for
    multiple tags, e.g. -s track -s title

For an example:

[davidp@supernova:~]$ ./retag-by-filename.pl --dry-run \
  --pattern="(?<track> \d+) \s - \s (?<title> .+ ) \s - \s (?<artist> .+ ) \.mp3" \
  /shared/music/Complete\ Albums/Oasis\ -\ The\ Masterplan/*.mp3
[01] Acquiesce by Oasis ()
[02] Underneath The Sky by Oasis ()
[03] Talk Tonight by Oasis ()
....

If I'd left out the --dry-run option, it would have retagged the files.

The tags which can be set, by including a named capture with the matching name,
are: track, title, artist, comment.